This invention generally relates to filters for disk based data storage systems, and more particularly, to multi-functional filter structures which include chemical and recirculation filtering components.
A disk drive is a data storage device that stores data in concentric tracks on a disk shaped medium. The reading of data from this medium usually entails spinning the medium about a central axis while positioning a transducer near a desired track of the medium to sense the data. The transducer provides an electrical signal representative of the sensed data to data processing circuitry within the disk drive which converts the electrical signal to a format that an attached host unit recognizes. (Disk drives can store data in any of a number of different forms, including magnetically and optically.)
A disk drive unit typically includes a housing that protects the workings of the drive from vapors, particulates and other contamination. These contaminants exist both inside and outside the disk drive housing and can have a deleterious effect on the operation of the dive. For example, particles and volatile gases inside the housing may cause problems such as stiction between the transducer and the disk, creation of thermal asperities, and even transducer crashes. To minimize such occurrences, the disk drive should include means for reducing the level of airborne particles and gases within its housing.
In addition, pressure gradients usually develop within a disk drive as a result of heating or cooling, by internal or external sources, or as a result of the acceleration and deceleration of the disks within the housing. Consequently, convection may drive air out of the drive housing or draw it into the housing through a predetermined path, such as through a filter and breather hole, or through undesirable paths such as leaks around gaskets and screw holes. In addition to contaminant movement by air flow or convection, contaminants may also move by diffusion. Diffusion is the result of a chemical gradient attempting to achieve equilibrium. Diffusion may occur inside the drive or between the inside and outside of the drive depending upon the presence of a chemical gradient.
The prior art includes a variety of filters designed to reduce the levels of undesired substances introduced into the housing of a disk drive, including multi-functional filters to filter undesired chemical vapors and particles. In many instances, these multi-functional filters are attached to the inside of the drive housing adjacent an opening in the cover or base plate. U.S. Pat. No. 5,030,260, issued Jul. 9, 1991, describes a specific example of a multi-functional filter for a disk drive assembly. This patent discloses an intricate multi-piece filter assembly comprising a number of component layers that filter incoming air. The components include external tape, diffusion plate, a first particulate filter, a first chemical adsorbent, a second chemical adsorbent, a second particulate filter, a bottom housing, including a second diffusion path, and bottom cover.
However, one disadvantage of the filter design described in the ""260 patent and other prior designs is that internal or recirculated vapors cannot access the chemical or carbon filters. The filter of the present invention advantageously overcomes the problem in the prior art filters. It includes a construction in which an integrated chemical filter element is combined with a recirculation filter element in a single integrated assembly that effectively and efficiently removes contaminants from the inside of the disk drive housing. It has a simple construction which minimizes the cost of fabrication and assembly while providing consistent and reliable performance.
In accordance with one embodiment of this invention, a filter assembly for a disk drive includes an outer shell through which gases flow in and out of the disk drive. The shell includes a hollow body position or housing with an end portion that extends into the disk drive. A first filter lies secured to the end portion of the housing and filters gases circulating and recirculating within the disk drive, entering into the disk drive, and discharging from it. The first filter is a gas pervious, tent or dome-like structure that defines a pocket and includes a layer of filtering media. Air and gases move through this layer, in and out of the pocket. Vapors within the recirculating gases further come in contact with a second filter, contained within the housing, that comprises an adsorbent body. By diffusion, at least a portion of these vapors are filtered by the adsorbent, thereby improving the quality of the recirculating air. Optionally, a third filter extends across an opening at the end portion of the housing and helps contain the second filter within the housing. By combining a recirculation and integrated chemical filter into a single, integrated unit, manufacture of the disk drive is improved, as two elements are combined into one, and the combined unit may be advantageously positioned at any desired location, whether at the inside or outside diameter of the disk, or in the disk drive base plate or top cover.